This invention relates to chains, and, in particular, to a sealed chain joint.
In chains used in ditching machines, earth scraping machines, and in other applications involving operation in an abrasive environment, it is desirable to protect the chain bearings (the wear surface between pin outside diameter and bushing inside diameter) by keeping the bearing lubricated and by preventing abrasive material from entering the bearing surface.
U.S. Pat. No. 2,411,207 "Hait", which is incorporated herein by reference, discloses a chain bearing seal in which a bushing is inserted through openings in the sidebars of a first link so that it extends past those first sidebars and provides a spacer between the sidebars of the first link and the sidebars of the second link. The bushing extensions also provide mounting surfaces for supporting a flexible seal. Laboratory tests of a chain having a sealed joint similar to that disclosed by Hait have shown that, when the chain is operated under load, there is a relatively high failure rate. The pins which hold the joints together tend to flex and contact the portions of the bushing which extend past the first sidebars. Since the extended portions of the bushing are cantilevered beyond the first sidebars and have no axial support, the contact with a flexing pin tends to cause failure of the bushings.
Another problem with the seal shown in the Hait reference is that it will fail to seal if the two sidebars against which it seals separate any appreciable axial distance. This type of seal failure can be expected when the chains undergo high stresses which cause the gap between the inner and outer sidebars to widen.
A main object of the present invention is to obtain many of the benefits of a sealed chain joint such as that shown in the Hait reference, while reducing the problem of bushing failure due to contact with the pin at unsupported portions of the bushing. Another object is to provide a sealing member which maintains its seal against the sidebars even when the sidebars tend to separate under load.